r bodies; that is, either they are
herbivorous, or they eat other animals which are herbivorous.

But for what constituents of their bodies are animals thus dependent upon
plants? Certainly not for their horny matter; nor for chondrin, the
proximate chemical element of cartilage; nor for gelatine; nor for
syntonin, the constituent of muscle; nor for their nervous or biliary
substances; nor for their amyloid matters; nor, necessarily, for their
fats.

It can be experimentally demonstrated that animals can make these for
themselves. But that which they cannot make, but must, in all known
cases, obtain directly or indirectly from plants, is the peculiar
nitrogenous matter, protein. Thus the plant is the ideal _proletaire_ of
the living world, the worker who produces; the animal, the ideal
aristocrat, who mostly occupies himself in consuming, after the manner of
that noble representative of the line of Zaehdarm, whose epitaph is
written in "Sartor Resartus."

Here is our last hope of finding a sharp line of demarcation between
plants and animals; for, as I have already hinted, there is a border
territory between the two kingdoms, a sort of no-man's-land, the
inhabitants of which certainly cannot be discriminated and brought to
their proper allegiance in any other way.

Some months ago, Professor Tyndall asked me to examine a drop of infusion
of hay, placed under an excellent and powerful microscope, and to tell
him what I thought some organisms visible in it were. I looked and
observed, in the first place, multitudes of _Bacteria_ moving about with
their ordinary intermittent spasmodic wriggles. As to the vegetable
nature of these there is now no doubt. Not only does the close
resemblance of the _Bacteria_ to unquestionable plants, such as the
_Oscillatorioe_ and the lower forms of _Fungi_, justify this conclusion,
but the manufacturing test settles the question at once. It is only
needful to add a minute drop of fluid containing _Bacteria_, to water in
which tartrate, phosphate, and sulphate of ammonia are dissolved; and, in
a very short space of time, the clear fluid becomes milky by reason of
their prodigious multiplication, which, of course, implies the
manufacture of living Bacterium-stuff out of these merely saline matters.

But other active organisms, very much larger than the _Bacteria_,
attaining in fact the comparatively gigantic dimensions of 1/3000 of an
inch or more, incessantly crossed the field of view.